1. Field of the Invention
The present invention relates to an image recording technique of ejecting ink to a recording medium such as paper and a film to record an image, and particularly to ink temperature control and ink circulation control techniques in an image recording apparatus.
2. Description of the Related Art
Conventionally, an inkjet image recording apparatus is frequently used in an output apparatus such as a facsimile and a copying machine. In a recording process of the inkjet image recording apparatus, the ink is ejected from plural nozzles formed in a recording head based on recording data and the ejected ink drops are appropriately fixed on a recording medium. Generally, viscosity is changed depending on a temperature in the ink used in the image recording apparatus. A shape and a size of the ink drop ejected from the nozzle vary when the ink viscosity is changed during the recording process (image recording). The variations in shape and size of the ink drop do not become troublesome in the case of the small change in ink viscosity. On the other hand, in the case of the large change in ink viscosity, uneven density and color difference are conspicuous in the image formed on the recording medium.
The ink is unstably ejected from the nozzle in the inkjet image recording apparatus when the ink temperature is out of a predetermined temperature range (out of recommended temperature range) in which the recording process can be performed. In the inkjet image recording apparatus, undesirably physicality of the ink is changed when the ink temperature increases excessively out of the predetermined temperature range. Additionally, in the inkjet image recording apparatus, when the ink temperature is out of the predetermined temperature range, possibly a satellite ink drop (unexpected small ink drop) and an ink mist in which the ink is ejected in the form of a mist are generated in addition to the main ink drop which is ejected from the nozzle and lands in the recording medium.
Therefore, in the inkjet image recording apparatus, in order to prevent the generation of the satellite or ink mist, it is necessary that the ink temperature be maintained in the predetermined temperature range to keep the ink viscosity constant.
For example, Jpn. Pat. Appln. KOKAI Publication No. 10-175308 discloses an inkjet printer. In a configuration of this inkjet printer, an ink tank in which a heater is provided and a print head are connected, and another ink tank and the print head are connected in order to return the ink supplied to the print head to the ink tank. In this inkjet printer, the ink is circulated while the ink temperature is controlled by the heater provided in the ink tank, and a recording operation (recording process) is performed by the print head while the ink temperature is kept within the set temperature range.